1. Technical Field
The present invention relates to a piezoelectric drive device having a piezoelectric actuator, and to an electronic device.
2. Related Art
Ultrasonic drive devices that use piezoelectric elements resistant to the effects of magnetism and are used as a drive device for driving the hands in a timepiece are known from the literature. Japanese Laid-Open Patent Publication JP-10-290579-A discloses such device as an example.
While the rotor starts rotating when a high frequency voltage (drive signal) is applied to the vibrator in order to start the ultrasonic drive device disclosed in JP-A-H10-290579 from a stopped state, a certain amount of time (acceleration time) is needed for the rotor to reach a prescribed speed. This acceleration time increases as the moment of inertia of the hands or other driven body increases. For example, when a speed reducing wheel train for slowing the speed of the rotor is located between the rotor and the hands, the moment of inertia of the wheel train and hands is relatively larger than the moment of inertia of the rotor, and the combined inertial moment of the rotor, a speed reducing wheel train, and the hands is from ten to one-hundred times larger than the inertial moment of the rotor alone.
Other arrangements have a speed increasing wheel train between the rotor and the hands so that the hands can be moved a prescribed angle even when the angle of rotor rotation is small. For example, this enables advancing the second hand the 6° angle equal to one second by advancing the rotor only 2°. The inertial moment imposed by a speed increasing wheel train is even greater than a speed reducing wheel train, and the acceleration time is therefore also longer.
The inertial moment is thus determined by the arrangement and form of the wheel train and hands, for example, the acceleration time of the rotor increases as the moment of inertia rises, the drive signal must therefore be applied to the vibrator (oscillator) longer, and power consumption by the ultrasonic drive device increases.